C+C on some Koopaling work.

[triptych]

if you're forcing yourself to a color limit, don't force yourself to only use certain parts of that palette in certain parts of the sprite (3 shades for skin, etc, like you mentioned). You essentially eliminate any chance of using each color to its fullest by doing that

throw some greens and blues in with the yellow as mid tones, and throw some yellows and oranges in with the blues and greens to highlight or help shade or something

you're making that palette infinitely more limiting than it needs to be